When I think of the 5:2 diet, I think of Dr Michael Mosley. Elsewhere in the world, other people may have different thoughts. Mosley started his investigations into intermittent fasting and calorie restriction for a BBC documentary, which aired in August 2012. I did a comprehensive report on the programme and the various fasting options that he explored (Ref 1). Much of the programme was set in America, where researchers at different centres were leading the way in testing different models of calorie restriction.
Mosley interviewed Professor Luigi Fontana at Washington University, who was researching calorie restriction every day. At the University of Southern California, Professor Valter Longo was looking at longevity in mice and Insulin-like Growth Factor (IGF 1). Longo advised Mosley to try a three and a half day fast, which he did and clearly didn’t enjoy. Chicago was the next stop where Dr Krista Varady was studying Alternate Day Fasting, which allowed women to consume 400-500 calories every other day and men 500-600. Mosley’s final destination was Baltimore where Professor Mark Mattson was also working with mice to better understand Alzheimer’s disease and the possibility that hunger could improve cognitive function. Mosley’s final experiment was to try something recommended by Mattson: 5 days of normal eating and 2 days at 600 calories a day. This was the pattern that Mosley personally felt most able to stick to and this was the one that has probably earned him a fortune. The Fast Diet (“Lose Weight, Stay Healthy, and Live Longer with the Simple Secret of Intermittent Fasting”) series of books were best sellers within a few months of the BBC documentary airing.
There doesn’t seem to be any trademark protection on 5:2 and so you’ll find a number of other books using the term (maybe Mattson should have trademarked it!) It wasn’t long before LighterLife® jumped on the band wagon to suggest that the fast days could be done with 4 of their 150 calorie sachets (Ref 2). LighterLife® funded the study that I’m looking at this week and one of the four authors on the study paper works for LighterLife®...
Some media headlines on March 19th 2018 declared: “5:2 diet could cut the risk of heart disease” (Ref 3). Others claimed: “5:2 dieters lose weight 'quicker' and may have healthier hearts – new study” (Ref 4). I think that this may be the first time I have seen a national newspaper undertake proper journalism on a diet/health story and not simply take the press release as fact. The UK Independent newspaper led with “5:2 diet does not reduce risk of heart disease, despite study's claims” (Ref 5).
The headline of the press release from the University of Surrey was: “Fasting diets reduce important risk factor for cardiovascular disease” (Ref 6). This was clarified in the first sentence of the press release: “Intermittent energy restriction diets such as the 5:2 diet clears fat from the blood quicker after eating meals compared with daily calorie restriction diets, reducing an important risk factor for cardiovascular disease...” The study summary is available, but not the full article (Ref 7). I’ve looked at the full article, so that you don’t have to!
The claim made in the press release is a quantum leap of which Carl Lewis would be proud. First, the study involved just 27 people. Second, the main part of the study was a diet and weight loss intervention, not an examination of blood fats. Third, the study measured the impact of one meal at the end of the weight loss intervention and thus even claiming a result after mealS, plural, is inaccurate. Fourth, the study assumed that the area under one 360 minute blood test curve is a risk factor for cardiovascular disease. Fifth, too much importance has been given to the one, barely significant, difference between the two diets after this one meal when every other measure showed no difference between the two diets (Ref 8). Finally, it has been assumed that the one, barely significant, difference found was the result of the diet pattern (energy restriction 2 days a week instead of every day of the week), but this was not the only difference between the two diets. The weight loss was faster with the 5:2 group. There was a significantly greater calorie deficit in the 5:2 group and the 5:2 group ended up consuming 80% of the carbohydrate intake of the other group. Did any of these make the tiny difference and not the diet pattern?
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